Study the prepubertal, pubertal, and postpubertal growth pattern of the mammary gland in relation to carcinogenesis. Investigate the induction of pubertal-type growth in "aging" mammary glands, and produce tumors in them by a chemical carcinogen, and induction of mammary tissue aging in immature rats to study the possibility of inhibition of mammary carcinogenesis. Study the biological and biochemical characteristis of mammary cells from nulliparous, pregnant, lactating, and multiparous rats in relation to their susceptibility or refractoriness to carcinogens.